1. Field of the Invention
The present invention relates to nonvolatile memory devices.
2. Description of the Related Art
Nonvolatile memory devices using resistive elements include phase-change random access memory (PRAM) devices, resistive random access memory (RRAM) devices, and magnetic random access memory (MRAM) devices. Nonvolatile memory devices store data using a variation in the state of a phase-change material such as a chalcogenide alloy, using a variation in the resistance of a variable resistive element, or using a variation in the resistance of magnetic tunnel junction (MTJ) films caused by a variation in the magnetic state of a ferroelectric material. In contrast, dynamic random access memory (DRAM) devices or flash memory devices store data using electric charge.
A phase-change material becomes either crystalline or amorphous by being heated and then cooled. A phase-change material in a crystalline state has a relatively high resistance, whereas a phase-change material in an amorphous state has a relatively low resistance. Thus, a phase-change material in a crystalline state may be defined as set data or data [0] and a phase-change material in an amorphous phase may be defined as reset data or data [1].